Final answer:
Selection impacts individuals, while evolutionary changes are observed at the population level. The correct response to the question is a) individuals, populations. This principle is part of the foundation of population ecology and evolution.
Step-by-step explanation:
Selection happens to individuals, but changes populations. The correct answer is a) individuals, populations. Natural selection acts on the level of individuals within a population, but the consequences of these selections are observed as changes in the overall genetic makeup of the population over time. This is a foundational principle of evolution, reflecting how characteristics that provide a survival or reproductive advantage become more common in the population across generations.
Population ecology is the study of how populations change over time and space and what factors affect their growth and decline. Population size, density, and distribution are central topics within this field because they impact the health of the population. Communities, on the other hand, involve interactions between populations of different species and are impacted by both biotic and abiotic factors.
The concept of evolutionary changes manifesting at the population level is crucial in understanding the broader impacts within communities and ecosystems, as it illustrates changes in a population's genetic structure which ultimately affect the composition and function of ecosystems.